Through a long lasting collaboration between Dr. Luis Barbeito, we have made major progress towards l unraveling how oxidative stress involving peroxynitrite formation causes the death of motor neurons in Amyotrophic Lateral Sclerosis (ALS). We have proposed a novel mechanism to explain how Zn-deficient SOD may cause motor neuron disease and have together coauthored 12 papers on these subjects over the past 7 years. Most recently, we have found that astroglia can play a pathogenic role in motor neuron degeneration. It is well known that reactive astrocytes surround degenerating motor neurons in ALS patients as well as in transgenic mice and rats over-expressing ALS mutant SOD-1. We found that peroxynitrite triggers a long-lasting phenotypic transformation in astrocytes, which promotes apoptosis of motor neurons cultured on the monolayers by mechanisms dependent on nitric oxide (NO) and peroxynitrite formation. Preliminary data implicates astrocytic synthesis of nerve growth factor (NGF) and its precursor form proNGF in triggering motor neuron apoptosis through activation of the "low affinity" NGF receptor p75NTR. We hypothesize that zinc-deficient SOD plus nitric oxide will activate astrocytes and contribute to the progression of motor neuron death through activating NGF/p75NTR signaling. To test this hypothesis, we propose to characterize whether zinc deficient SOD can make astrocytes reactive and induce NGF synthesis and secretion. The pro-apoptotic activity of the different NGF forms will be tested on cultured motor neurons and in vivo studies will be performed to analyze whether blockade of NGF/p75NTR pathway in G93A transgenic mice affect disease progression. These additional studies will provide important insight into astrocytes could contribute to the progressive death of motor neurons in ALS. Halting the progressive death of motor neurons in ALS could be of huge clinical significance.